simple sparql query not working, dates comparison

Here is Your Sparql Query as URL to the DbPedia sparql endpoint. Which just seems to work. Maybe there was a temporary overload of the system that made it timeout, or maybe you have to add additional information on how you operate your query?

It's because your query is too hard for the DBPedia endpoint to answer without adversely impacting other users of the service.

As DBPedia is a well known public SPARQL endpoint it gets very heavily used so the people who host it have it configured to impose strict limits on how long a query can run for so that rogue users don't make the service unusable for others.

In your case your query will take a long time because you ask something that has a lot of initial results (592299 to be precise) and then apply a FILTER over it. FILTER is quite expensive in SPARQL especially when doing string manipulation and date comparison. AFAIK the DBPedia timeout is something fairly low like a few seconds and the endpoint simply cannot finish your query within that time because it takes too long to apply the FILTER.

Note - Here's the query I used to see how many results the first portion of your query was returning:

PREFIX ont: <http://dbpedia.org/ontology/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT COUNT(*) 
WHERE 
{
   ?person ont:birthDate ?date .
   ?person foaf:name ?name   
}

If you really want to have fun with DBpedia, you need to load it into your own triple store.

If you've got a machine with an above-average amount of memory (like my 24GB Windows workstation or a high-memory extas large instance in the AMZN cloud) it's pretty easy to load DBpedia into the open source edition of Virtuoso -- the DBpedia public endpoint uses the commercial version of the same software, so you should get very much the same results.

I've loaded data sets of similar size into an 8GB laptop and had success, although the loading takes most of a day.

DBpedia has some anomalies and Virtuoso is more tolerant of broken RDF than some other products, so you might have some challenges with other triple stores. I know Ontotext has a special edition of DBpedia that has been cleaned to work with OWLIM-SE.

Note also that the version of DBpedia in the public endpoint is incomplete: it lacks the "Wikipedia pagelinks" data set, which I find particularly fruitful.

I guess missing the trailing } is just a typo?

Your query is quite expensive, requiring to check through the birthdates of all people in Wikipedia and apply the filter you specify, hitting less that 1-in-365 persons.

Try starting with a LIMIT 1 and see from there. This works for me, and should now be cached:

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX ont: <http://dbpedia.org/ontology/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?name ?date (bif:substring(STR(?date), 1, 4) AS ?year) WHERE {

   ?person ont:birthDate ?date .
   ?person foaf:name ?name .

   FILTER ( (fn:string-length(STR(?date)) = 10)  && (bif:substring(STR(?date), 9, 2) = '05')  && (bif:substring(STR(?date), 6, 2) = '02') && (?date > "1868-01-01"^^xsd:date) && (?date < "2005-01-01"^^xsd:date) )
}
LIMIT 10

Increment the limit or fiddle with the range (as a cheap version of "offset") until you're happy with the answers you get.